The present invention relates to hinge joints in general, and more particularly to improvements in hinge joints which can be used with advantage in the seats of motor vehicles or the like, for example, to pivotally and adjustably connect the back to the lower portion of a seat. Still more particularly, the invention relates to improvements in hinge joints of the type wherein a second component is pivotably connected to a first component by a coupling device including a shaft which is rotatably journalled in one of the components and can be rotated by a hand wheel, by a lever or the like, a gear train including mating gears which are provided on the two components and surround the shaft, and an eccentric which is provided on the shaft and can move the gear on one of the components radially into more or less pronounced mesh with the other gear.
The eccentric can constitute the frustum of a cone which is integral with the shaft and is surrounded by a complementary frustoconical internal surface of one of the gears. It is further known to bias the eccentric and/or the one gear axially so as to maintain the internal surface in contact with the eccentric. Reference may be had to the commonly owned European patent application Ser. No. 0 048 294 to Walk et al. which discloses a hinge joint wherein the frustoconical internal surface is provided in a spur gear which is rigid or integral with the stationary component of the hinge joint. The shaft is rotatably and axially movably journalled in a disc which is riveted to the spur gear of the stationary component. The shaft is further rotatably and axially movably journalled in an end plate which is rigidly connected to the pivotable component, and the shaft is biased axially by a dished spring so as to maintain the frustoconical internal surface of the spur gear in contact with the periphery of the frustoconical eccentric. The purpose of the spring is to ensure that the spur gear mates with the internal gear of the pivotable component without play. To this end, the internal surface is in static frictional engagement with the eccentric when the pivotable component of the hinge joint is held in a selected position so that the spring cooperates with the spur gear and with the eccentric to eliminate play between the gears of the two components as well as to eliminate play in the bearings between the components and the shaft. Static friction is reduced to sliding friction as soon as the shaft is positively rotated by a hand wheel, by a lever or in another way in order to change the inclination of the pivotable component. At such time, the force which is generated by the spring and acts upon the eccentric in the axial direction of the shaft is opposed by the axial component of the force which is attributable to eccentricity of the eccentric and has a component acting in the axial direction of the shaft counter to the direction of action of the spring force. The eccentric is then caused to move axially of the surrounding frustoconical internal surface against the opposition of the spring to thus allow for a reduction of the force which is required to rotate the shaft in order to change the inclination of the second component. It has been found that the eccentric is likely to move axially to such an extent that it bears against a stop and thereby generates frictional forces which must be overcome by the person rotating the shaft. Such additional or excessive axial shifting of the eccentric is likely to take place under the weight of the back of a seat which embodies the hinge joint and/or in response to the action of the force with which the occupant of the seat in a motor vehicle leans against the back of the seat. The generation of such additional forces renders it more difficult to manually adjust the inclination of the back and renders it necessary to expend more energy if the inclination of the back of a seat is changed by a motor.